1. Field of the Invention
The present invention relates to a noise restraint apparatus for a digital camera, and in particular to noise restraint in long time exposure operations such as night-view imaging and astrophotography imaging.
2. Description of the Related Art
When a long time exposure operation is carried out in a digital camera which has an imaging device such as a CCD, there is a problem that a dark output by a certain picture element of the imaging device, becomes bigger than that of other picture elements due to the influence of the dispersion of dark current in each picture element on the imaging device, so that the dark output by a certain picture element turns out as a bright point in a dark area on the image.
Even for an optical black output, which is obtained when a partly shaded CCD is used, the dark current component is not able to be cut and removed, so that an image having generally increased brightness and damaged image quality is obtained.
Japanese unexamined patent publication (KOKAI) No. 2001-78084 discloses a noise detecting apparatus that detects the temperature of the CCD which rises due to continuous use, and warns the operator of the possibility that the dark current might influence the image, when the temperature of the CCD rises above a standard temperature. This is the usual method of detecting fixed pattern noise due to dispersion of dark current in each picture element.
However, the above-discussed conventional noise detecting apparatus does not restrain the occurrence of noise.